Modern wind turbine rotor blades are built from fiber-reinforced composites combined with core members, such as balsa wood or plastic foam.
For example, EP 2 123 431 A1 describes a method for manufacturing a rotor blade using a vacuum assisted resin transfer molding (VARTM)-process. In a first step of the manufacturing process, fiber material is laid onto a lower part and an upper part of a mold, respectively. The fiber material is secured in place by vacuum applied from beneath. Then, mold cores are covered in vacuum bags and are placed in the lower part of the mold together with a web (also known as shear web). Next, the upper part of the mold, together with the fiber material, is turned 180 degrees about its longitudinal axis and put into place so that the mold is closed. In a further step, vacuum is applied to the space between the mold cores and the mold. Then, resin is injected. When the resin has set, the mold cores are removed, the mold is opened and the cured blade is removed from the mold.
The webs typically employed in the process are manufactured in a separate process. According to said separate process, plywood plates are covered with a fiber material. The fiber material is injected with a resin. Once the resin has set, the cured web comprising a fiber reinforced resin and a plywood core can be taken out of a corresponding mold.
For some applications, the webs are required to have a recess at one end. The recess is configured to ensure a smooth transfer of loads into and out of the rotor blade, i.e. the recess avoids stress concentrations due to abrupt changes in the geometry. The recess is machined into said end of the web. In this process about 60-100 kg of web material need to be removed which requires substantial manpower and causes waste.